As we know, the second half of the 1930's was a very dangerous period for foreign Communists in Moscow. Some parties, like the Polish one, had virtually their entire leadership imprisoned and shot. One foreign Communist who was in Moscow in 1934-38 was Ho Chi Minh. Today we regard his name as virtually synonymous with Vietnamese Communism, but in the 1930's he had his share of enemies in the Communist movement, and could quite easily have fallen victim to the purges:
"Ironically, Comintern intervention was just as likely to divide as to unite communist parties. Nguyen Ai Quoc (Ho Chi Minh), a founding member of the French Communist Party, believed that socialism was indissoluble from the liberation of Indochina from French colonial rule. In the mid-1920s he was something of a paragon for ECCI [Executive Committee of the Communist International], making a brilliant speech to the Fifth Congress in July 1924, in which he accused the French and British communist parties of failing to give support to the peoples of the French and British colonies, especially in Africa. In 1925 he set up the Vietnamese Revolutionary Youth League, the first Indochinese communist organization, in Guangzhou with CCP support. With the shift to ‘class against class’, members of the League in Tonkin set out to ‘proletarianize’ the party, and this led to the arrest of many activists in central and southern Vietnam. The Central Committee, however, together with the Annam regional committee, was unhappy at this radical turn. In 1930, Hồ effected an uneasy rapprochement between what had become two separate parties, but he did not endear himself to ECCI, which accused him of failing to impose a clear ‘class line’. By the time he enrolled at the Lenin School in October 1934, he no longer held a leadership position in the Indochinese Communist Party (the Comintern had forbidden the creation of a separate Vietnamese party). *Holed up in Moscow for four years, he was suspected of ‘nationalist errors’ and breaches of security, and probably survived only because Indochina was not a priority for Soviet leaders.* [my emphasis--DT] Surprisingly, the shift away from the policies of the ‘third period’ did not improve his standing: it merely reopened splits inside the party, with first Tran Phu and then Ha Huy Tap, both trained in Moscow, condemning Ho for capitulating to bourgeois nationalism. Despite the Comintern’s return to a policy that prioritized national liberation over social revolution, Ho only slowly regained influence. It was mainly his success from 1941 in building the Viet Minh, which was committed to organizing all Vietnamese ‘whether workers, peasants, rich peasants, landlords, or native bourgeoisie’ to liberate their country from Japanese military occupation and French colonial rule, that sealed his dominance.6 As this suggests, ECCI may have been the ultimate arbiter of internal quarrels, yet its policies could be deeply divisive within national parties..."
https://books.google.com/books?id=ZMd7AgAAQBAJ&pg=PT236
Suppose Ho had indeed fallen a victim of the purges? Who would lead the Vietnamese Communists? Ha Huy Tap, one of Ho's critics mentioned above, and General Seceretary from 1936 to 1938, was executed by the French in 1941
https://en.wikipedia.org/wiki/Hà_Huy_Tập as was his successor Nguyen Van Cu.
https://en.wikipedia.org/wiki/Nguyễn_Văn_Cừ_(revolutionary) Truong Chinh
https://en.wikipedia.org/wiki/Trường_Chinh is a possibility, but perhaps too closely associated with the Chinese Communists. ("Truong Chinh" was in fact a pseudonym, meaning "Long March," after Mao's famous march.) Other Vietnamese Communist leaders of the 1940's (Vo Nguyen Giap, Pham Van Dong, etc.) first became well-known as the result of their association with Ho, and I am not sure how they would have fared in his absence.
The basic strategy of the Viet Minh--to rally various political, religious, etc. groups under the nationalist banner, while at the same time making sure that the Communists kept control--was an obvious one for Vietnamese Communists under the conditions of World War II and the postwar era. But I am not sure that any alternative leadership could have managed it as successfully as Ho did in OTL.